Magnetic disk drives are widely used in computers and data processing systems for storing information in digital form. Digital information is stored in magnetic disk drives as binary-encoded data which is magnetically recorded on a recording surface of a magnetic disk by selective magnetic polarization of regions of the surface of the disk. The recording surface of the magnetic disk is typically divided into narrow annular regions termed "tracks" of different radii. The tracks are assigned numbers to provide addresses for locating data on the recording surface.
Data stored on a magnetic disk is accessed as the disk rotates by means of a transducer called a read/write head. To read data from a rotating magnetic disk, the read/write head produces electronic read signals in response to the passage of magnetic polarized regions on the recording surface of the magnetic disk close by the read/write head as the disk rotates. To write data onto a rotating magnetic disk, the read/write head generates magnetic fields, capable of polarizing regions of the recording surface disk passing close by the head, in response to the imposition of electronic write signals on the read/write head.
In a conventional disk drive assembly, the read/write heads are secured to the distal ends of head suspension members. Several suspension members may be mounted in parallel, one to each side of each of a stack of disks. The proximal end of each suspension member is attached to an actuator arm. The actuator arm in turn is connected to a servo or stepper motor. The magnetic heads of the drive are moved to selected tracks on the disks by the servo or stepper motor via the actuator, its arms, and the connected head suspension members.
There are various methods of attaching head suspension members to an actuator arm. Such methods include glue, screws, clamps, and staking.
In one known staking method, two head suspension members are attached to the end of an actuator arm by means of two staking members having short tubular stems each of which is aligned through a hole in the head suspension member and into a through hole in the end of the actuator arm. The stems of the staking members are thereafter forcibly expanded within the structural material of the shelf segment of the actuator arm by driving a ball bearing through the stem tubes.
This particular method, although effective, has several limitations. The most significant limitation in expanding the stem of the staking members within the structural material of the arm is the possibility of cracking the arm during the staking procedure. Cracking of the arm often occurs despite the given thickness of the arm. The nature of the assembly employed in this method channels the force of the staking procedure in the direction in which the ball is forced through the staking members. If there is even a slight structural defect in the material of the actuator arm or if the actuator arm is deflected in the direction of the force applied to the ball, i.e., the axial direction, the arm will crack. This cracking results in defective assemblies and is a costly problem in mass manufacturing the actuator arm assemblies. The staking procedure is one of the last assembly procedures to take place in the manufacturing process. If the arm cracks during the staking procedure, the entire semi-complete multiple arm actuator assembly must be discarded at a significant cost.
In response to these limitations, another method of staking was developed in which only one staking member was employed. In this method, two head suspension members are first attached to opposing sides of the flange of the staking member, and then the staking member is subsequently secured to the actuator arm in a single staking procedure. The force exerted by the staking procedure is still channeled directly into the structural material of the arm, and some deflection of the arm occurs. Thus, cracking is still a limitation. As a result, a significant percentage of the actuator arm assemblies still have to be discarded.
The problem related to the cracking of the actuator arm becomes more severe with an anticipated change in structural materials to ceramics. The metallic materials presently used expand and contract slightly when exposed to changes in temperature due to a metallic material's inherent coefficient of thermal expansion. These expansions and contractions hinder the accurate placement of the magnetic heads on the disks. Because ceramic materials have a minimal coefficient of thermal expansion, there is an anticipated change in actuator arm materials to ceramics. This change will increase the accuracy of head placement by minimizing thermal expansions and contractions. However, this change creates problems in attaching head suspension members to ceramic actuator arms by any type of staking method. Expanding a staking member within an actuator arm formed from a ceramic material shatters the arm. The cracking problem described is a major hindrance in the development of technology related to ceramic actuator arms.